fix bug in neural_style_transfer example for image_dim_ordering=tf (#3715)
fix bug in neural_style_transfer example for image_dim_ordering=tf (#3715)

* fix bug in neural_style_transfer example for image_dim_ordering=tf

* fix PEP8 mixed space and tab

nebw/keras,keras-team/keras,dolaameng/keras,keras-team/keras,kuza55/keras